1. Field of the Invention
An apparatus and method for driving a liquid crystal display (LCD) device is provided.
2. Discussion of the Related Art
Generally, a LCD device can adjust the light transmittance of liquid crystal cells according to a video signal so that an image is displayed. An active matrix type LCD device has a switching element formed for every liquid crystal cell and can display a moving image. A thin film transistor (TFT) can be used as a switching element in the active matrix type LCD device.
FIG. 1 illustrates a related art apparatus for driving an LCD device.
As shown in FIG. 1, the related art apparatus for driving an LCD includes an image display unit 2 including liquid crystal cells formed in each region defined by the first to n-th gate lines GL1 to GLn and the first to m-th data lines DL1 to DLm. A data driver 4 supplys analog video signals to the data lines DL1 to DLm. A gate driver 6 supplys scan pulses to the gate lines GL1 to GLn. A timing controller 8 aligns externally input data RGB and supplies them to the data driver 4, generates data control signals DCS that control the data driver 4, and generates gate control signals GCS to control the gate driver 6.
The image display unit 2 includes a transistor array substrate, a color filter array substrate, a spacer, and a liquid crystal. The transistor array substrate and the color filter array substrate face each other and are bonded to each other. The spacer uniformly maintains a cell gap between the two substrates. The liquid crystal is filled in a liquid crystal area prepared by the spacer.
The image display unit 2 includes a TFT formed in the region defined by the gate lines GL1 to GLn and the data lines DL1 to DLm, and the liquid crystal cells connected to the TFT. The TFT supplies analog video signals from the data lines DL1 to DLm to the liquid crystal cells in response to the scan pulses from the gate lines GL1 to GLn. The liquid crystal cell is comprised of common electrodes facing each other by interposing the liquid crystal therebetween and pixel electrodes connected to the TFT. Therefore, the liquid crystal cell is equivalent to a liquid crystal capacitor Clc. The liquid crystal cell includes a storage capacitor Cst connected to a previous gate line to maintain the analog video signals filled in the liquid crystal capacitor Clc until the next analog video signals are filled therein.
The timing controller 8 aligns the externally input data RGB to be suitable for driving of the image display unit 2 and supplies the aligned data to the data driver 4. Also, the timing controller 8 generates the data control signals DCS and the gate control signals GCS using a dot clock DCLK, a data enable signal DE, and horizontal and vertical synchronizing signals Hsync and Vsync that are externally input, so as to control each driving timing of the data driver 4 and the gate driver 6.
The gate driver 6 includes a shift register that sequentially generates scan pulses, for example, gate high pulses in response to a gate start pulse GSP and a gate shift clock GSC among the gate control signals GCS from the timing controller. The gate driver 6 sequentially supplies the gate high pulses to the gate lines GL of the image display unit 2 to turn on the TFT connected to the gate lines GL.
The data driver 4 converts the data signal, aligned from the timing controller 8, into analog video signals. This conversion is in response to the data control signals DCS that are supplied from the timing controller 8. The analog video signals, which are supplied to the data lines DL, correspond to one horizontal line per one horizontal period. The scan pulses are supplied into the gate lines GL. In other words, the data driver 4 selects a gamma voltage having a predetermined level depending on a gray level value of the data signal Data and supplies the selected gamma voltage to the data lines DL1 to DLm. The data driver 4 then inverses polarity of the analog video signals supplied to the data lines DL in response to a polarity control signal POL.
The related art apparatus for driving an LCD device has a relatively slow response speed due to characteristics such as the inherent viscosity and elasticity of the liquid crystal. In other words, although the response speed of the liquid crystal may be different according to the physical properties and cell gap of the liquid crystal, it is common that the rising time is 20 to 80 ms and the falling time is 20 to 30 ms. Because this response speed is longer than one frame period (16.67 ms in National Television Standards Committee (NTSC)) of a moving image, as shown in FIG. 2, the response of the liquid crystal proceeds to the next frame before a voltage being charged on the liquid crystal cell reaches a desired level.
Since the image of each frame displayed in the image display unit 2 affects the image of the next frame, as shown in FIG. 3, motion blurring occurs in the moving image due to perception of a viewer.
The related art apparatus and method for driving an LCD device causes motion blurring degradation in contrast ratio, and, in turn, degradation in display quality.
In order to prevent motion blurring from occurring, an over-driving apparatus, which modulates a data signal to obtain the fast response speed of the liquid crystal, has been suggested.
FIG. 4 is a block diagram illustrating a related art over-driving apparatus.
As shown in FIG. 4, the related art over-driving apparatus 50 includes a frame memory 52 that stores data RGB of a current frame Fn, a look-up table 54 that generates modulated data for obtaining the fast response speed of the liquid crystal by comparing the data RGB of the current frame Fn with data of a previous frame Fn−1 stored in the frame memory 52, and a mixing unit 56 that mixes the modulated data from the look-up table 54 with the data RGB of the current frame Fn.
The look-up table 54 lists modulated data that converts a voltage of the data RGB of the current frame Fn into a higher voltage to obtain the fast response speed of the liquid crystal, thereby adapting to a gray level value of an image moving at the fast speed.
Since a voltage higher than an actual data voltage is applied to the liquid crystal using the look-up table 54 as shown in FIG. 5, the fast response speed of the liquid crystal is adapted to a target gray level voltage until a desired gray level value is actually obtained.
Accordingly, the related art over-driving apparatus 50 can reduce motion blurring of a display image by accelerating the response speed of the liquid crystal using the modulated data.
However, the related art LCD device fails to obtain a clear image due to motion blurring occurring in boundaries A and B of each image as shown in FIG. 6 even though the image is displayed using the over-driving apparatus. Since luminance increases between the boundaries A and B of the image to have a tilt, motion blurring still occurs even though the liquid crystal is driven at high speed.